It does sound like it is dying. You are correct that keeping it too wet causes rots. Too dry is also a problem. Sometimes it helps to feel the soil to see if it needs watering or not. If you are not keeping it too wet or dry then perhaps some disease is involved. Also, that plant prefers some morning sun and afternoon shade as the full brunt of the summer sun it really hard on it.
You might want to take a sample and/or a photo to your County Extension Office to see if they can diagnose the specific cause. The horticulture agent's name is Daphne Richards.
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